Cytokines are relatively low molecular weight, pharmacologically active proteins that are secreted by cells for the purpose of altering either their own functions or those of adjacent cells. Cytokines are important regulators of hematopoiesis. They exert their actions by binding to specific receptors on the cell surface. Among the cytokines are a large number of interleukins as well as growth and colony-stimulating factors. Interleukin-5 (IL-5) is a critical cytokine for regulation of growth, activation, maturation, and survival of eosinophils, a type of leukocyte, and their release from the bone marrow. Eosinophils have been implicated in the pathogenesis of certain diseases ("eosinophilic syndromes") characterized by long-term chronic inflammation of tissues, such as the lungs in the case of asthma or the muscles in the case of eosinophilia myalgia. Other eosinophilic syndromes in addition to these include allergic rhinitis and atopic dermatitis. Eosinophils have also been noted as a component of cellular infiltrates of malignant tumors. Eosinophils are attracted to sites of wounding or inflammation, where they undergo a process of activation. Because eosinophils play a seminal role in the pathogenesis of asthma, particularly the late-phase reaction of asthma, and other inflammatory and/or allergic conditions, IL-5 signal transduction is of clinical importance.
In humans, IL-5 is selective in specifically promoting eosinophil and basophilic differentiation and maturation. Blood and tissue eosinophilia is a characteristic abnormality in allergy and asthma and convincing evidence implicates IL-5 as the key cytokine regulating this selective eosinophilic inflammation. Thus, inhibition of IL-5 production or effector function will abolish the eosinophilic component in asthma and other eosinophilic diseases, likely preventing further tissue damage caused by release of eosinophil-specific inflammatory mediators and potentially providing clinical benefit. Indeed, it has been demonstrated neutralizing IL-5 with a monoclonal antibody can completely inhibit bronchoalveolar eosinophilia caused by allergen challenge in guinea pigs, mice, and monkeys. A correlation exists between pulmonary eosinophilia and asthma in man and it is clear that selective inhibition of IL-5 can block airway hyperresponsiveness in animal models.
Asthma is characterized by episodic airways obstruction, increased bronchial hyperresponsiveness, and airway inflammation. An association has been shown between the number of activated T cells and eosinophils in the airways and abnormalities in forced expiratory volume in one second (FEV1), a measure of pulmonary function, increased bronchial responsiveness, and clinical severity in asthma. It has been documented that both interleukin-5 (IL-5) mRNA and protein levels are increased in bronchial biopsies from both atopic and intrinsic asthmatics.
IL-5 interacts with cells via the IL-5 receptor (IL-5R) on the cell surface. The IL-5 receptor is a heterodimer of .alpha.- and .beta.-subunits. The IL-5 receptor.alpha.-subunit is specific to IL-5R, whereas the .beta.-subunit is common to IL-3, IL-5, and granulocyte/macrophage colony-stimulating factor (GM-CSF) receptors. The human IL-5 receptor (IL-5R) is expressed in vitro on eosinophils, basophils, and B lymphocytes, although its role on B cells remains in question. Besides a membrane anchored form, two forms of soluble human IL-5R.alpha. are produced. Only the membrane form of the .alpha. chain is complexed with the .beta. chain, which is required for signaling.
The link between T cell derived IL-5 and lung eosinophilia is further strengthened by the observation that increased levels of IL-5 receptor.alpha. mRNA are also found in bronchial biopsies from asthmatics and that the eosinophil is the predominant site of this increased IL-5R.alpha. expression. Further, the subset of eosinophils that express the membrane bound form of the IL-5 receptor inversely correlates with FEV1 while the subset expressing the soluble form of the receptor directly correlates with FEV1. These observations suggest that IL-5 receptor.alpha. isoform expression is of central importance in determining clinical prognosis. The soluble form of the receptor may be serving a beneficial role in asthmatic patients. It is therefore presently believed that an effective therapeutic approach to preventing eosinophilia in asthma and other eosinophilic syndromes would entail selective inhibition of membrane but not soluble IL-5 receptor expression. In addition, there are several animal and lung explant models of allergen-induced eosinophilia, late phase airway responses, and bronchial hyperresponsiveness which collectively support a link between IL-5 and airway eosinophilia and decreased pulmonary function.
Several approaches to inhibition of IL-5 function have been tried. Chimeric, humanized and other interleukin-5 (IL-5) monoclonal antibodies (mAbs), and pharmaceutical compositions and therapeutic methods are disclosed in WO 96/21000. Ribozymes for cleaving IL-5 mRNA are disclosed in WO 95/23225. A 16mer phosphodiester oligo deoxynucleotide with two phosphorothioate linkages, targeted to IL-5 mRNA, was used to inhibit IL-5 secretion by human peripheral blood mononuclear cells. Weltman and Karim, Allergy Asthma Proc., 1998, 19, 257-261; September-October 1998. Methods of treating airway disease by administering essentially adenosine-free antisense oligonucleotides to the airway epithelium are disclosed in WO 96/40162. IL-5 and IL-5 receptor are among the antisense targets disclosed.
Thus there remains a long felt need for compositions and methods for modulating IL-5 signal transduction, particularly in the treatment and prevention of asthma and other reactive airway disease.